The present invention is directed to light modulators, and in particular to light modulators known as deformographic displays. Generally, in this type of display a non-conductive base member has a plurality of symmetrically arranged holes formed therein. In some instances the holes extend partially through the base member, whereas in other instances the holes extend completely through the base member. A reflective membrane is then stretched over the surface of the base member. Provision is made to collect charge in the respective holes by electrostatic, electromagnetic or other means. The portion of the membrane over a hole in which charge has been collected is deformed or deflected in the hole. This results in the selective formation of dimples in the membrane. Light impinging on the dimpled surface is phase modulated in accordance with the depths of the dimples. Therefore, an image can be reproduced in a phase modulated form of the reflected light from the dimpled surface in accordance with which holes have charge therein.
In any event, the display structure is relatively difficult to fabricate and complex control circuitry which is housed external to the base member, is needed. In the type of base member where the holes extend partially therethrough, a plurality of external connections are required to deposit charge in the holes. In the type of base member where the holes extend completely therethrough, other means, for example an electron gun, is needed to deposit charge in the holes or on the membrane. Other known base members need to be housed in evacuated glass envelopes or the like, which increases cost and fabrication problems.
U.S. Pat. No. 3,796,480 to Preston, Jr., et al discloses a membrane light modulator wherein a collodian membrane coated with a pluality of spaced-apart, reflective and conductive strips is stretched across a support member comprised of a glass plate having an array of holes formed therein. A separate electrode is located underneath each column of holes. Individual electrical signals are applied from an external source to each of the strips and each of the electrodes to produce electrostatic deflections in the portions of the membrane over the holes. The structure itself appears difficult to fabricate and requires an external connection to each strip and to each electrode.
U.S. Pat. No. 3,701,586 to Goetz discloses a deformographic display in which a membrane is formed over a base member comprised of a microchannel plate which has the holes extending completely therethrough. Charge is placed on the membrane over a given hole by means of an electron gun. Accordingly, a complex and what appears to be difficult to fabricate display device results.
Other known deformographic displays include U.S. Pat. No. 3,858,080 to Wohl which discloses a deformographic storage display device, and U.S. Pat. No. 3,479,109 to K. Preston, Jr., which discloses a display in which a membrane is stretched over a glass base member.
According to the present invention, a deformographic display is disclosed in which the base member is a semiconductor, rather than a non-conductor, and in which the control circuitry can be fabricated directly in the semiconductor substrate using MOSFET and/or bipolar technology. Accordingly, the external control connections are reduced to a minimum resulting in a more efficient and easily fabricated display.